Solar System Log by Andrew Wilson, published 1987 by Jane's Publishing Co. Ltd.

Mariner 9 was the second in the pair of identical spacecraft launched in 1971 to orbit Mars. The first spacecraft, Mariner 8, failed to reach Earth orbit.

Based on a wide octagonal structure, these vehicles used a bipropellant propulsion system with a fixed thrust of 136 kilograms for orbital insertion around Mars. All scientific instrumentation on the spacecraft was mounted on a movable scan platform underneath the main bodies. The span of the spacecraft over its extended solar panels was 6.9 meters.

Following an en route midcourse correction on 5 June 1971, Mariner 9 ignited its main engine for 915.6 seconds on 14 November 1971 at 00:18 UT, becoming the first human-made object to enter orbit around a planet other than Earth. Initial orbital parameters were 1,398 x 17,916 kilometers at 64.3° inclination.

The primary goal of the mission was to map about 70 percent of the surface during the first three months of operation. The dedicated imaging mission began in late November, but because of the major dust storm at the planet during this time, photos taken prior to about mid-January 1972 did not show great detail. Once the dust storm had subsided, Mariner 9 began to return spectacular photos of the deeply pitted Martian landscape, showing for the first time such features as the great system of parallel rilles stretching more than 1,700 kilometers across Mare Sirenum.

The vast amount of incoming data countered the notion that Mars was geologically inert. There was some speculation on the possibility of water having existed on the surface during an earlier period, but the spacecraft data could not provide any conclusive proof.

By February 1972, the spacecraft had identified about 20 volcanoes, one of which, later named Olympus Mons, dwarfed any similar feature on Earth. Olympus Mons, part of Nix Olympica-a "great volcanic pile" possibly formed by the eruption of hot magma from the planet's interior-is 25 kilometers high and has a base with a diameter of 600 kilometers. On 11 February 1972, NASA announced that Mariner 9 had achieved all its goals. By the time of last contact at 22:32 UT on 27 October 1972, the spacecraft had mapped 85 percent of the planet at a resolution of 1 to 2 kilometers, returning 7,329 photos.

Key Dates

30 May 1971: Launch

14 Nov 1971: Mars Orbit Insertion

Status: Successful

Fast Facts

Mariner 9 was the first spacecraft to orbit another planet. Though launched 11 days after the U.S.S.R.'s Mars 2, it arrived at Mars 13 days earlier than the Soviet spacecraft.

It was the first spacecraft to detect water vapor on Mars (over the south pole).

Mariner 9 pictures were used to select landing sites for the two Viking missions (above) of the mid-1970s.